SEQUENCE POLYMORPHISM IN THE EPSTEIN-BARR-VIRUS LATENT MEMBRANE-PROTEIN (LMP)-2 GENE

Latent membrane protein 2A (LMP-2A) is expressed in Epstein-Barr virus transformed B lymphocytes in vitro and has been detected in various t ypes of EBV-associated malignancies. LMP-2A interferes with membrane s ignal transduction through phosphorylation of its hydrophilic N-termin al domain and binding of the cellular tyrosine kinases encoded by fyn and lyn. In vitro, the domain can block calcium influx and participate in signal transduction inducing cytokine production. These two activi ties are differently affected by site-directed mutagenesis of potentia lly phosphorylated amino acid residues. Several potential tyrosine pro tein kinase recognition motifs have been identified including an antig en recognition motif (ARAM). ARAMs are activated by tyrosine phosphory lation that enables binding of tyrosine protein kinases such as lyn an d fyn. To assess the importance of potential sequence variation in nat ural EBV infection and in tumourigenesis, the sequence of the LMP-2A N -terminal domain was determined in 28 EBV isolates, including 14 fresh tumour isolates. Comparison of the corresponding sequences with the p rototype B95 strain indicates that LMP-2 is generally conserved with a few base pair changes resulting in conservative amino acid changes in an occasional isolate. However, five single-base loci were frequently mutated, resulting in three patterns of sequence polymorphism in exon 1 of LMP-2A. The patterns did not segregate with EBV Type 1 or Type 2 and were detected in both lymphoid and epithelial tissues. Four of th e most frequent mutations at loci 166627, 166750, 166796 and 166805 (c odons 23, 63, 79 and 82) could potentially affect tyrosine protein kin ase binding motifs. The pivotal tyrosines (codons 74 and 85) and leuci nes (codons 77 and 88) of the LMP-2 ARAM were not affected in any of t he isolates, suggesting that ARAM function is important for EBV infect ion in vivo. However, the interspacing positions 79 and 82 were distin ct in more than 50% of the isolates. These prevalent polymorphisms cou ld influence interaction of the LMP-2 cytoplasmic domain with specific cellular ligand proteins.